Robert,
For the Campi's you probably need to find an old school race shop that support vintage racing, they would be most liekly to have or know of someone that can work on mag alloy wheels. It's not a simple process, as the wheels have to go through heat treating.
If I were you I'd install spacers behind your current rears and move them out a littls. If you have the longer GT5 studs installed they should be long enough to do that. Many GT5's came with spacers from the factory.
Julian
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